In the operation of a process such as HF catalytic alkylation of isobutane with propylene and/or butylenes, relief gases containing HF and light hydrocarbons, such as from the HF catalyst storage tank, the reactor settler, the product hydrocarbon-HF recontactors, the depropanizer refrigerated overhead accumulator, and the like, cannot be vented or sent to the flare because of ecologic problems with HF. HF passes through the flare unchanged.
This HF must be removed from these streams in order to minimize corrosion in the relief lines, as to the flare and to minimize atmospheric pollution.
This invention employs an HF acid relief drop-out drum to accumulate and remove any liquid hydrocarbons present in the relief fluids or produced in the system, as by condensation of the light hydrocarbon vapors. This liquid removal protects the acid relief neutralizer vessel in that, under normal operating conditions, substantially only non-condensible hydrocarbons containing HF are charged to the neutralizer. When, under upset operations liquid hydrocarbon, such as propane, enters the neutralizer, evaporation of the propane can cause freeze-up of even the caustic solution, resulting in high pressure build up in this system with disastrous results. High pressure can rupture the vessels and fire and explosion can result from the released hydrocarbons.
Purge gas, such as nitrogen or sweet (sulfur-free) fuel gas, as for example natural gas, is applied to the system. When there are no relief gases charged to the operation, the purge gas sweeps through the drop-out drum and the neutralizer to prevent moisture from entering the system, e.g., via the flare unit, due to temperature changes, e.g., night-time cooling drawing in moist air. The moisture entering can dissolve HF forming corrosive liquid which can damage piping and vessels of the system. The purge gas prevents this problem. Purge gas also passes continuously through the by-pass line around the neutralizer.
In order to provide greater safety, it has occurred to me that heating of the circulating neutralizing agent and the provision of a vapor relief safety by-pass of the neutralizing zone, which has a high pressure rupture disc, would provide such additional safety which would avoid the hazards of a disastrous explosion.
Accordingly, an object of this invention is to provide a method and means for fluids handling.
Another object of this invention is to provide a means for preventing explosions in a fluids handling system.
A further object of this invention is to provide an improved knock-out drum-caustic treating system in an HF acid alkylation operation.
Other aspects, objects, and the several advantages of this invention are apparent from the study of this disclosure, drawing, and the appended claims.